The present invention relates to a method for controlling the fuel/air ratio of an internal combustion engine in which the output signal of a first lambda probe, which is arranged in the exhaust gas passage of the internal combustion engine in front of a catalytic converter, is fed to a controller which has a proportional-plus-integral characteristic. The controller gives off a setting variable for the fuel/air ratio, and the controller is fed a further signal which is obtained from the output signal of a second lambda probe arranged behind the catalytic converter and acts on the control circuit of the first lambda probe.
In order to obtain exhaust gases which are as free of injurious substances as possible, control devices for internal combustion engines are known in connection with which the oxygen content in the exhaust gas canal is measured and evaluated. For this purpose, oxygen measurement probes, so-called lambda probes, are known, which operate for instance in accordance with the principle of ion conduction by a solid electrolyte as a result of an oxygen partialpressure difference corresponding to the oxygen partial pressure present in the exhaust gas, the probes give off a voltage signal which, upon change from oxygen deficit to oxygen surplus or vice versa, exhibits a change in voltage.
The output signal of the lambda probe is evaluated by a controller which, in its turn, adjusts the fuel/air mixture again via an actuating member.
By the control of the fuel/air ratio, it is desired primarily to reduce the injurious portions of the exhaust gas emission of internal combustion engines.
By means of a second lambda probe which is arranged behind the catalytic converter, the signal of the first lambda probe is corrected, since the probe is subject to aging phenomena.
Despite this superimposed control, the aging phenomena of the first lambda probe, are not sufficiently corrected. This leads to irregularities in the formation of the mixture.